- Replace 4 hardcoded samples with 200 workouts across 10 activity types
- Add deleteAllWorkouts() to reset sample data cleanly
- Auto-insert samples on launch when fewer than 200 exist

- Paginate workout loading in batches of 50 with loadMoreWorkouts()
- Group workouts by month/year with section headers
- Add searchable filter by activity type name
- Show loading indicator at bottom for infinite scroll

- Add ActivityGraphView (Swift Charts line/area graph with dimming overlays)
- Add RangeSliderView (two-thumb slider for selecting trim range)
- Rewrite WorkoutEditView: graph, slider, time labels, activity picker
- Expand HealthKitManager with HR/energy/distance queries and realistic sample data
- Add destructive action warning to save confirmation
- Remove WorkoutAddView (not a use-case)